The Crissy Field lagoon feels like it’s always been there, with constant tidal movements and shifting sand making every day, or every hour, different.
But what you and more than a million other annual visitors see is an artificial recreation of natural wetlands, filled in by the Army in the latter half of the 1800s, then restored in the 1990s.
The brackish lagoon, where spring water from the Presidio’s hills and seasonal rain meets San Francisco Bay’s salty tides, has two distinct parts. There’s the 18-acre tidal marsh itself, where flocks of pelicans hang out and snowy egrets stalk about the mudflats.
There’s also a channel that connects the marsh to the bay, the direction of the flow depending on the tide. It cuts through East Beach, sometimes creating a deep pool in the middle of the beach for wading children and frolicking dogs. Other times, it flows fast and direct from the marsh to the bay, leaving much of the beach dry and intact.
But nature doesn’t always align with the modern contours and uses of Crissy Field. The tidal marsh fills with sediment, and the connecting channel tends to wander east, parallel to the shore.
The farther it shifts, “the less efficient it is at draining and scouring the accumulated sediments,” says Golden Gate National Recreation Area spokesperson Julian Espinoza. More mud means more problems for water health, for native oysters trying to make a comeback, and for small fish that the pelicans, herons, and other birds hunt in the shallows.
But Crissy Field is engineered not just for wildlife but humans – promenades, bridges, roads, and parking lots limit nature’s pathways. So the National Park Service has to intervene. One way it does so is by reshaping Crissy Field’s East Beach at least once a year to keep the connecting channel open.
At times, the channel re-opens naturally on its own, Espinoza notes, but periodic sand sculpting with heavy equipment “re-sets” the cycle, allowing a faster exchange of salty bay water into and out of the marsh.
A reshaping of the beach took place exactly one year ago. I took photos once a week – before, during, and after – to show how powerful natural (and human) forces continue to act upon this amazing corner of our city.
Before the excavation
In August and September of 2023, the channel emerged from the tidal marsh and meandered east across East Beach, leaving a spit of sand like a barrier island.
During the excavation
The heavy equipment was on the scene in early November to push the beach around.
After the excavation
One week later, the sand berm that the earth mover pushed into place had already crumbled. The channel water continued to flow north, but water had pushed through the berm to the east, as well.
